In general, in order to manufacture a semiconductor integrated circuit, various thermal processes such as a deposition process, an annealing process, an oxidization and diffusion process, a spattering process, an etching process, a nitriding process and so forth are performed several times repeatedly on a silicon substrate such as a semiconductor wafer.
In this case, in order to maintain electric characteristics of the integrated circuit and throughput of the products to high level, the above-mentioned various thermal processes should be performed on the entire surface of the wafer more uniformly. For this purpose, because the progress of the thermal process remarkably depends on the temperature of the wafer, the temperature of the wafer should be uniform throughout the entire surface thereof at high accuracy in the thermal processing.
In order to maintain the temperature of the wafer uniform throughout the entire surface thereof, various methods are known. For example, in one method used in a single-wafer-type thermal processing system, a placement table on which a semiconductor wafer is placed is rotated so that occurrence of unevenness in temperature is avoided.
FIGS. 1 and 2 show two examples of thermal processing systems in the related art.
In FIG. 1, in a processing chamber 2 in which a vacuum can be produced, a thin placement table 4 is set which is supported on a bottom of the chamber 2, on which table a semiconductor wafer W is placed. A shower head part 6 for providing a necessary processing gas such as a deposition gas into the processing chamber 2 is set on a top of the processing chamber 2. Further, on a bottom of the processing chamber 2, a transmitting window 8 made of a quarz glass, for example, is mounted in an airtight manner, and, beneath it, a plurality of heating lamps 10 such as halogen lamps, for example, are mounted on a rotational table 12 which also serves as a reflective plate. The wafer W is heated from the rear side thereof by means of radiant heat from the heating lamps 10 while the rotational table 12 is rotated. Thereby, it is attempted to heat the surface of the wafer W uniformly.
In a thermal processing system shown in FIG. 2, a gas providing nozzle 14 for providing a processing gas is provided in a side wall of the processing chamber 2 on one side, while a discharge mouth 16 for producing a vacuum is provided on the other side. Transmitting windows 18 and 20 made of a quarz glass are provided on a top and a bottom of the processing chamber 2. Further, above the upper transmitting window 18 and beneath the lower transmitting window 20, heating lamps 22 are disposed, and, thereby, the wafer W is heated from both top and bottom sides thereof. The placement table 4 is supported on a rotational shaft 24 passing through a bottom plate of the processing chamber 2 in an airtight manner, and, as a result, is rotatable. In this system, while the wafer W is rotated, the wafer W is heated from both sides, and, thus, it is attempted to heat the surfaces of the wafer W uniformly.
In the system shown in FIG. 1, the heating lamps 10 are rotated. However, this system has a configuration such that a gate valve 26 is provided in the side wall of the processing chamber 2 for bringing in the wafer W. Accordingly, there is not a necessarily sufficient isotropy in view of temperature. As a result, it may not be possible to achieve a sufficiently uniform temperature distribution throughout the surface of the wafer W.
In the system shown in FIG. 2, as the wafer W itself is rotated, isotropy in temperature of the side wall of the processing chamber 2 may be not so problematic. However, as the upper transmitting window 18 has a very high temperature due to radiant heat from the heating lamps 22 and from the wafer W, especially in a case of a deposition process, a deposition film or a reaction by-product may adhere to this transmitting window 18, by which the luminous intensity transmitted by the transmitting window 18 may be changed, and, as a result, repeatability may be degraded, or particles may be generated therefrom. Further, although N2 purge such as providing an inert nitrogen gas little by little toward the rear surface of the placement table 4 is performed, there is also a possibility, even fewer, that such a problem as the adherence of a deposition film or a reaction by-product occurs for the lower transmitting window 20.
Further, this problem of adherence of a deposition film or a reaction by-product may also occur for the inner wall of the processing chamber 2 as it has a high temperature. Accordingly, it is necessary to perform cleaning of the processing chamber 2 frequently.
Furthermore, each of the above-mentioned transmitting windows 8, 18 and 20 has a large thickness for the purpose of increasing a pressure resistively thereof. As a result, the heat capacity thereof is large, and, thereby, controllability of the temperature of the wafer W therethrough is degraded. Further, the distance between the heating lamps and wafer W increases as the thickness of the transmitting window increases. As a result, the directivity of the heating lamps is degraded.
In order to improve the directivity of the heating lamps, it is effective to shorten the distance D between the surface of the wafer W and the heating lamps (22, for example in FIG. 2) so that diffusion of the radiant heat of the heating lamps is reduced.
For example, FIGS. 3A and 3B are graphs showing relationships between the directivity of the heating lamps and the above-mentioned distance D. FIG. 3A shows the directivity for D of 55 mm, while FIG. 3B shows the directivity for D of 35 mm. Each curve in the figures represents a temperature dependency on the wafer for a respective heating lamp. As can be seen from the figures, in the case of FIG. 3A, the peak of each curve is gentle. Accordingly, the number of heating lamps contributing to heat a specific zone of the wafer is large, and, thus, the directivity is low. In contrast thereto, in the case of FIG. 3B, as the peak of each curve is sharp, the number of heating lamps contributing to heat a specific zone of the wafer is small, and thus, the directivity is high.
Thus, in order to improve the directivity of the heating lamps, it is preferable to shorten the distance D. However, in a case where thermal processing of the wafer is performed in a vacuum atmosphere (pressure-reduced atmosphere), a thickness t of the transmitting window 20 made of a quarz glass should be on the order of 30 through 40 mm for a diameter thereof on the order of 400 mm, for example, so as to secure a high pressure resistivity of the transmitting window 20. Thereby, the directivity of the heating lamps are degraded, and, also, the temperature controllability is degraded as a result of the heat capacity of the transmitting window 20 being increased due to the increased thickness t thereof.
In order to solve this problem, the pressure resistivity of the transmitting window 20 may be increased as a result of shaping it to a dome shape having an approximately hemisphere shape, for example, as shown in FIG. 4. However, in this case, although it is possible to reduce the thickness of the transmitting window 20 itself to the order of 10 through 20 mm, the total height H of the dome-shaped transmitting window 20 is on the order of 60 through 70 mm. Accordingly, this method cannot solve the problem in that the above-mentioned distance D should be shortened.
FIGS. 5 and 6 show another example of a thermal processing system in the related art. FIG. 5 shows a general configuration of the thermal processing system, and FIG. 6 shows a plan view illustrating an arrangement of heating lamps of the thermal processing system. As shown in FIG. 5, in a processing chamber 102, a ring-shaped placement table 104 is provided. The periphery of the semiconductor wafer W on the bottom side thereof is made contact with the inner circumference of the placement table 104 on the top side thereof, and, thus, the wafer W is supported by the placement table 104. This placement table 104 is fixed on a top end of a cylindrical leg part 106 which is supported by a bottom of the processing chamber 109 via a ring-shaped bearing part 103. Thus, the placement table 104 is rotatable along a circumferential direction of the cylindrical leg part 106.
A rack 110 is provided on the inner wall of the leg part 106 along the circumferential direction of the leg part 106. Further, a driving shaft 114 of a driving motor 112 provided beneath the chamber 102 projects upward through the bottom of the chamber 102 in an airtight manner. The driving shaft 114 has a pinion 116 fixed on the top thereof which is engaged with the above-mentioned rack 110. Thereby, the leg part 106 and the placement table 104 integral therewith are rotated. Further, a flat transmitting window 118 made of a quarz glass, for example, is provided on the top of the processing chamber 104 in an airtight manner. Further, above the transmitting window 118, a plurality of heating lamps 120 are provided. Then, by means of radiant heat from the lamps 120, the wafer W is heated to a predetermined temperature. As a result of the placement table 4 being rotated at a time of the heating, the wafer W placed on the placement table 104 is heated while it is rotated. Accordingly, the temperature of the wafer W is made uniform throughout the surface thereof.
In this system, the heating lamps 120 include, as shown in FIG. 6, for example, approximately spherical lamp bodies 122, and reflective plates 124 provided at the rear side of the lamp bodies 122 and formed to be depressed. Thereby, the radiant heat can be efficiently used. Further, in order to enable supply of large power, the lamp bodies 122 include therein filaments 126 extending toward the wafer W spirally. Such a type of lamp bodies are called ‘single-end type lamp bodies’. In this case, the plurality of heating lamps 120 are arranged so as to cover the top surface of the above-mentioned semiconductor wafer W.
FIGS. 7 and 8 show another thermal processing system in the related art. In this system, instead of the sphere-liked lamp bodies 122 described above, rod-like lamp bodies 128 are employed in heating lamps 130. At the rear side of the lamp bodies 128, reflective plates 132 each having a sectional shape of approximately hemisphere are disposed. In each lamp body 128, a spirally wound filament 134, for example, is contained so as to extend along a longitudinal direction of the lamp body 128, and electric terminals 136 are provided on both ends of the lamp body 128. Such a type of lamp body 128 is called a ‘double-end type lamp body’. The heating lamps 130 are disposed in parallel with predetermined intervals.
When the sphere-shaped lamps 120 with the depressed reflective plates 124 are used as shown in FIGS. 5 and 6, directivity and controllability of the radiant heat are satisfactory. However, in this structure of each lamp 120, the amount of radiant heat in horizontal directions is large, and it is reflected so as to be directed toward the wafer, and energy is lost each time of the reflection. Accordingly, a large amount of energy is lost.
In contrast thereto, when the rod-shaped lamps 130 shown in FIGS. 7 and 8 are used, a large amount of radiant heat is directly irradiated to the wafer. Accordingly, the energy loss is relatively small. However, in this case, each lamp body 128 should cover a relatively large area of the surface of the wafer. Further, because the lamp body 128 is disposed across the wafer, the directivity thereof is degraded. Accordingly, it is difficult to make the temperature of the wafer uniform at high accuracy.
Further, in order to improve the directivity of the radiant heat, a distance D between the surface of the wafer W and the heating lamps 120, for example (see FIG. 5), should be shortened so that diffusion of the radiant heat is made smaller, as described above with reference FIGS. 3A and 3B. Also in this case, it can be considered to employ a dome-shaped transmitting window as the transmitting window 118 in order to reduce the thickness of the transmitting window, as described above with reference FIG. 4. However, as mentioned above, by such a method, the problem cannot be solved substantially.